| .. SPDX-License-Identifier: GPL-2.0 |
| |
| ============ |
| Paravirt_ops |
| ============ |
| |
| Linux provides support for different hypervisor virtualization technologies. |
| Historically, different binary kernels would be required in order to support |
| different hypervisors; this restriction was removed with pv_ops. |
| Linux pv_ops is a virtualization API which enables support for different |
| hypervisors. It allows each hypervisor to override critical operations and |
| allows a single kernel binary to run on all supported execution environments |
| including native machine -- without any hypervisors. |
| |
| pv_ops provides a set of function pointers which represent operations |
| corresponding to low-level critical instructions and high-level |
| functionalities in various areas. pv_ops allows for optimizations at run |
| time by enabling binary patching of the low-level critical operations |
| at boot time. |
| |
| pv_ops operations are classified into three categories: |
| |
| - simple indirect call |
| These operations correspond to high-level functionality where it is |
| known that the overhead of indirect call isn't very important. |
| |
| - indirect call which allows optimization with binary patch |
| Usually these operations correspond to low-level critical instructions. They |
| are called frequently and are performance critical. The overhead is |
| very important. |
| |
| - a set of macros for hand written assembly code |
| Hand written assembly codes (.S files) also need paravirtualization |
| because they include sensitive instructions or some code paths in |
| them are very performance critical. |
